1. Field
The present Application for Patent relates to line drivers, more particularly, to active impedance matched transmission cable drivers.
2. Background
Although the range of communication applications using wireless continues to increase, there are instances and applications for which hard wire transmission lines or cables remain in use. Example reasons include certain there being applications in which means for wireless communication may not be available, or may be impractical or not cost efficient.
There are quality metrics for communication by transmission cables, one being the efficiency in transferring energy from a communication signal source at one end of a cable to a destination, typically a communication signal receiver, at the other end of the cable. There are various known means for improving such efficiency. These include, for example, high conductivity transmission cable, with good quality dielectric, to minimize resistive power loss, power being lost in heating instead of being delivered to the load. Another known means is to maintain a match between the output impedance of the output amplifier (also called, for example, a “buffer,” “line driver” or “drive buffer”) driving the transmission cable and the characteristic impedance of the transmission cable, and with the impedance of the load at the terminating end of the cable, typically termed a “load impedance.” Such matching obtains maximum efficiency in the ratio of the power dissipated at the load, to the power dissipated in the source, and minimizes power loss from reflection of signal energy back from the load toward the source, and/or from positions along the length of the cable back toward the source. The principles of electromagnetic wave propagation by which impedance matching reduces such power loss are well known and, therefore, except where pertinent to understanding an aspect of a present embodiment, further detailed description is omitted.
Conventional line drivers are therefore typically designed and constructed with an output impedance matched, at least within an acceptable range, to the intended load impedance. To provide adaptability and to better maintain power transfer efficiency in actually installed transmission line systems, conventional line drivers may include means for automatic adjustment of their output impedance. However, typically this automatic impedance adjustment requires additional circuitry, and this has cost, in terms of chip real estate and power consumption.
Potentially amplifying the cost of the circuitry for automatically adjustable output impedance are other objectives and goals pertaining to the driving of signals into transmission cables, each having a separate cost in chip real estate and, and in chip power consumption.